The present invention relates to substrates for printed circuit boards and, more particularly, to materials which may be used as printed circuit board substrates and methods for using such substrates in the fabrication of printed circuits.
Printed circuits have long ago replaced wire circuits in the vast preponderance of applications. A printed circuit makes it possible to economically and reliably produce many copies of highly complicated circuits, which take up relatively little space.
To produce a printed circuit, a thin sheet of conductive metal, typically copper or aluminum, is made to adhere to one or more faces of a substrate. The substrate is typically in the form of a sheet of appropriate thickness and mechanical properties used to preserve the shape of the conductive layer and give the structure strength. The conductive layer is subsequently exposed to a printing process which imprints onto the conductor surface the precise image of the circuit design. Etching techniques are then used to remove certain portions of the conductor layer so as to leave the precise circuit desired.
The choice of substrate is of great importance since its electrical properties significantly affect the performance and efficiency of the circuit, especially at high frequencies. This will be increasingly the case in the future as faster logics, such as higher switching frequencies and denser conductive patterns, will increasingly require a substrate of low dielectric constant and low dissipation losses.
A variety of substrates are in current use, among them glass epoxy, tetrafluoroethylene or Teflon.RTM. and Duroid.RTM..
While such substrates provide adequate mechanical properties, their electrical properties leave something to be desired. Specifically, these substrates have dielectric constants and dissipation factors which in certain applications be sufficiently high to adversely affect the performance and efficiency of the printed circuit. In addition, these substrates are relatively costly and of relatively high density, thereby raising both the cost and the weight of the finished printed circuits.
There is thus a widely recognized need for, and it would be highly desirable to have, printed circuit boards substrate which have significantly lower dielectric constants and dissipation factors than those of commonly used substrates and which, in addition, is less costly and of lower density.